Process of spray drying a solution of a monopersulfate and a boron compound



U i d $e a e 1 2,886,412 PROCESS OF SPRAY DRYI N G A SOLUTION OF AMONOPERSULFATE AND A -BORON COMPOUND Donald B. Lake, Grand lsland, andStephen E. Step'hanou, Lewiston,.N.Y., assignors to E'. I; du Pont deNemours and Company, Wilmington, Del., a corporation of Delaware NoDrawing. Application-January 31, 1956 Serial vNo. 562,599

5 Claims. (Cl. 23-114 This invention relates to improvements in themanu- ,facture of solid alkali metal monopersulfates. It relates, moreparticularly, to an'improved methodiof recovering solid alkali metalmonopersulfates from'aqueous solution.

The acid salts of monopersu'lfuric or Caros acid, H580 have been knownfor many years. They are readily prepared by the partial neutralizationof the acid with a carbonate or hydroxide, usually thatof an alkalimetal, followed by recovery of thesolid by evaporation of the water.It-may benoted that bothhydrogen ions in the acid cannot be replaced byneutralization, attemptsat such replacement merely leading todecomposition of the monopersulfate ion.

The acid salts are unstable at'high'temperatures and the evaporation ofwater therefrom as accomplished heretofore is a tedious processwhich'may require between sev eral hours and several weeks. Such a process isobviously unacceptable commercially. The solids finally recovered are,moreoveninthe form of-hard crusts or agglomerates which must bepulverized beforehuseor further proc= essing.

An object of this invention is, consequently, to provide an improvedmethod for the recovery of alkali metal and ammonium monopersulfatesfrom their aqueous solutions.

Another and particular object is provision of a commercially acceptablemethod for recovering sodium monopersulfate from aqueous solution.

A further object is provision of a method for recovering sodiummonopersulfate from aqueous solution in a finely-divided condition.

The above-mentioned and yet further objects are are achieved inaccordance with this invention by a process in which certain chemicalsare added to the monopersulfates, in clear solution or in a slurry, andthe resulting mixture is passed through a spray drier.

The chemicals added to the monopersulfate in the spray-drying procedureare inorganic compounds of boron such as borax, boric acid and boricanhydride. The quantity of boron compound utilized will depend to someextent on the particular monopersulfate salt that is being dried but ingeneral a weight of about 1l0%, based on the total weight of the slurryor solution, suflices. Additional improvements can sometimes be obtainedby addition to the mixture of a commercial wetting agent such as thealkyl aryl sulfonate of an alkali metal. The improvement given by thewetting agent is, however, slight, and employment of the material ispurely optional.

The behavior of a monopersulfate in spray drying is partially determinedby the cation present. Potassium or ammonium monopersulfate solutions orslurries may be spray dried directly with about 90% recovery of theactive oxygen. Some of the product, however, generally adheres to thewalls of the spray drier. In the mildest cases, this behavior results indecomposition of the product with loss of active oxygen. In extremecases, the

drier is completely clogged. When boron compounds comprising betweenabout 1 and 2% by weight of solueither benzene or toluene.

' ice tion or slurry are added to the solution, substantially of theactive oxygen can be recovered. Higher percentages of additive canbeused but are unnecessary.

The behavior of sodium monopersulfate is' quite dif ferent, solutions ofthis compound cannot be spray-dried without the help of an adjuvant. Thesodium'salt always clogs the drier with consequent'loss'of all activeoxygen; The boron additives mentioned'above are, however," quiteeffective in passing this 'salt through the drier.

The quantity'of additives needed with sodium monopersulfate is somewhatlarger than that added to the potassium or ammoniumsaln- A weight ofadditive comprising between about 1 and 10% .by weight of the solutionor slurry should be' utilized with 510% preferred. Since the quantity ofboron additive canbe varied not only with a particular monopersulfatebut also with the different salts, it may properly and broadly bereferred to in all cases as an amount effective to .passthe salt througha spray drier? The weight of adjuvant employed is calculated from thetotal weight of the slurry or solution dried and may perhaps beunderstood from a consideration of the methods of preparing thecompound. As noted above, the monopersulfates are generally formed bypartially neutralizing a solution of 'monopersulfuric acid contain= ingsulfuric acid. Sulfates and bisulfates are consequently producedsimultaneously with' the monopersulfates. The sulfates andbisul'fates'partially precipitate from the solution yielding a slurrywhich may then be spray dried after the process of this invention. Thisslurry is the one referred to above. Alternatively, the slurry may befiltered to yield'the clear solution also mentioned' above. The solutionyields aproduct higher in active oxygen content than the-slurry doesbut, since the sulfate and bisulfate impurities may. be..desinable,..they are usually retained. While the monopersulfate samplesdried by the instant process may be referred to generically assolutions, it will be understood that solid precipitate may also bepresent.

As noted, a hydrocarbon sulfonate wetting agent may optionally beemployed, particularly with sodium monopersulfate. Preferred sulfonatesare the aryl alkyl sodium or potassium salts containing a 12 carbonchain attached to a sulfonated benzene nucleus. The chain may, however,consist of 3-15 carbons and the nucleus may be About 0.51% of thesulfonate is preferred, the weight again calculated from the totalWeight of solution or slurry. These agents may also be used withpotassium and ammonium monopersulfates with some improvement in results.

The type of spray drier used in the practice of the invention isimmaterial. A rotating disk spray drier was employed in theillustrations given below but other driers, employing for example theprinciple of atomizing the solution tobe dried, are perfectlysatisfactory. In all cases the product has the advantage that its bulkdensity is less than the bulk density of a solid monopersulfate obtainedin any other manner, e.g. by pulverizing solid crusts. Low bulk densityis especially important in one major utility of the solids, bleaching.It enables the salts to be mixed with solid detergents, themselves oflow density, without the danger of settling or separation under theinfluence of gravity.

The spray-drying adjuvants of this invention have been discussedprimarily with reference to solutions of the monopersulfates of thealkali metals. They can be used with other monopersulfates as well, thatof calcium for example. Of the alkali metal and ammonium salts, those ofsodium, potassium and ammonium are the most important and representpreferred embodiments of the invention.

I II 2,83 2 I II I I I I I I ,m

I Thel eqfcllow somerejxmiples which iilus trateztheprac- 'for nau tralsailfates werqincludedinthe 501115011 0: slum v I i ceiof t e invenfibmAll-percentag s the examp es 1 w v n M iY PwPertiESI I Infill 5125111 II I I I I I I I I I are weightpQ:In?en ta geIs;v I l I I v v I I Iinlettcmperaturc wa s' about 600 640"- E and the outlet I I I I 1 I, I II I :tempera'tlire was about 140 150'F. 'Pressures'vilerefy I I I I I II I 5 "ambient: i'Ihe diskz waszrotatedat a spead of;:about i I j I I tI t I I f; A series :Qf SI U IIiQS containingdissolved sodium mono.-30300-50300 I I I v I v I I I I I I I I P D Ej was I fad f m)COIIIVEIHIiOiHIII i a ngisgw I I The wetting agent; optionally employedin some run's V 1 I I :sp r aydrying apparatus; 'lnslde :such, apparatusthe, liqmdi was a commercial ag'nt believed to, be the' Isqdium: saltof. I i I j I gmlxtur'ei 'strikes a xapifily rota tin'g iskj h h d PI II an, acid consisting pf 3 12 carbon alkyl chain attached} 101 I I, I, II I the r d 1 3 pray f 5 18113. The drSpersipn is flln: 1:0 a.sulfonated benzene .nueleus; I The; active oxygefi con-z I I I I I Icompletely dried y c ing streflmfof hotlairr T e I tnt'repo'rtedinzthepi'oduct isuncorrctedformoisture -i I t I II t I Tpr'oduct-fall'sto-the floor of ihe drienand is carried into a p -esegm I5.6%,; v I I I I I I I I I I I coll'estor whenteit isrsmovedig w;; i ,I:I I i I I I I I I I I I Theresults obtained from tl 1eruns are reportedinvthe= I 523 5 52212:6232; 5 332; ziii i;b a mom, V i 'SIOme cases"Such Phosphates persulfate'of the group consisting of the alkalimetal-and I I I Table I I I I I I I I I I I I I I I I ammoniumm0nopersu1fates,- the step comprising supply! II II II II P dG t"oanhydrideandborax.---: I I I j m m jg g I If'f 2.:"I'h prwass of ciaim'lvsizn zvlcwingaisoluticzvn of .3:; I I fiatey fPgmlIltyw -0xvgen Remarks p I i mDn persuIfate ,I I I I 1, I, I 1 1 I I. I II I'weightofthe bol'bnempotlfldisfsupplidtfiflJQSOlUfiDBg f: 4; The processcfclaim ,lemployingasolufionof 109; by wig h t qf a boron I IIIII I I-sopv L N I compound of thegrduponsistingofihorisiacidfljoriw fi w

1. IN THE PROCESS OF SPRAY DRYING A SOLUTION OF A MONOPERSULFATE OF THEGROUP CONSISTING OF THE ALKALI METAL AND AMMONIUM MONOPERSULFATES, THESTEP COMPRISING SUPPLYING TO SAID SOLUTION ABOUT 1-10% BY WEIGHT OF ABORON COMPOUND OF THE GROUP CONSISTING OF BORIC ACID, BORIC ANHYDRIDEAND BORAX.